You will always be limited by the speed of the USB bus. Its likely USB 2.0, so throughput should be limited to 480 Mb/s. But that's probably not your bottleneck. SD Cards have different speeds. The speeds are detailed in a "speed class" (such as "Class 4" (4 Mb/s) or "Class 10" (10 Mb/s)). UHS Class 3 will achieve 30 Mb/s, which should be pretty responsive for non-large files (with "large files" like videos). What class of card do you have?
– user9341Oct 20 '14 at 8:45

1 Answer
1

Yes, running apps from an SD card is slower. That's why as a developer you can prevent your app from being moved if you have concerns about performance (guess that's mainly a potential issue with games).

HOWEVER, you usually don't see a big impact with more "static" apps like your podcast app. So my guess would be that it's the files that slow you down. I had a similar issue with a geo logging tool.

Guess you'll only know for sure if you try moving it or clean up your library.